Fin patterns with varying spacing without fin cut

ABSTRACT

Methods of forming semiconductor fins include forming first spacers on a first sidewall of each of a plurality of mandrels using an angled deposition process. A second sidewall of one or more of the plurality of mandrels is masked. Second spacers are formed on a second sidewall of all unmasked mandrels. The second sidewall of the one or more of the plurality of mandrels is unmasked. The mandrels are etched away. Fins are formed from a substrate using the first and second spacers as a mask.

BACKGROUND Technical Field

The present invention generally relates to semiconductor devicefabrication and, more particularly, to forming semiconductor fins usinga directional sidewall deposition process and sidewall image transfer.

Description of the Related Art

Sidewall image transfer (SIT) is used in the fabrication of, e.g., finfield effect transistors (FinFETs) to create semiconductor fins thathave a feature size that is smaller than the smallest available featuresize in a lithographic process. SIT forms sidewalls on a mandrel andthen removes the mandrel. The sidewalls are used as a mask for asubsequent etch that defines the semiconductor fins. However, thisprocess creates pairs of fins—one on each sidewall of the mandrel. If agiven fin is not part of the design, it is removed after formation byusing a fin cut mask.

As fin pitch shrinks, fins are formed closer to one another. Theinherent variations of misalignment of mask deposition produce a yieldproblem for close fin pitches, resulting in either incomplete removal ofunneeded fins (when the fin cut mask fails to cover the unneeded fins)or an unintentional cut of device fins (when the fin cut mask encroachesonto the device fins).

SUMMARY

A method of forming semiconductor fins includes forming first spacers ona first sidewall of each of a plurality of mandrels using an angleddeposition process. A second sidewall of one or more of the plurality ofmandrels is masked. Second spacers are formed on a second sidewall ofall unmasked mandrels. The second sidewall of the one or more of theplurality of mandrels is unmasked. The mandrels are etched away. Finsare formed from a substrate using the first and second spacers as amask.

A method of forming semiconductor fins includes forming first spacers ona first sidewall of each of a plurality of amorphous silicon mandrelsusing an oxygen gas cluster ion beam. A finless region is masked byforming a mask directly on a second sidewall of one or more of theplurality of mandrels. Second spacers are formed on a second sidewall ofall unmasked mandrels using an oxygen gas cluster ion beam. The finlessregion is unmasked. Spacer material is anisotropically etched fromhorizontal surfaces of the mandrels after unmasking the finless region.The mandrels are etched away. Fins are formed from a substrate using thefirst and second spacers as a mask, such that no fins are formed in thefinless region.

A method of forming semiconductor fins includes forming first spacers ona first sidewall of each of a plurality of amorphous silicon mandrelsusing an oxygen gas cluster ion beam that is angled between about 10°and about 80°. A finless region is masked by forming a mask directly ona second sidewall of one or more of the plurality of mandrels. Secondspacers are isotropically formed on a second sidewall of all unmaskedmandrels using an oxygen gas cluster ion beam. The finless region isunmasked. Spacer material is anisotropically etched away from horizontalsurfaces of the mandrels after unmasking the finless region. Themandrels are etched away. Fins are formed from a substrate, comprising anitride pad layer directly on a semiconductor layer, using the first andsecond spacers as a mask, such that no fins are formed in the finlessregion.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 2 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 3 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 4 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 5 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 6 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 7 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 8 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles;

FIG. 9 is a cross-sectional diagram of a step in forming fins inaccordance with the present principles; and

FIG. 10 is a block/flow diagram of a method of forming fins inaccordance with the present principles.

DETAILED DESCRIPTION

Embodiments of the present invention employ a directional sidewalldeposition process to form sidewalls on only one side of a mandrel. Forregions where no fin is needed, the mandrels are then masked while asecond directional sidewall deposition process is used. In this manner,sidewalls are created only on those sides of the mandrels thatcorrespond to device fins. No fin cut is then needed, as no extraneousfins are created.

Referring now to FIG. 1, a cross-sectional view of a step in forming asemiconductor device is shown. A pad layer 104 is formed on asemiconductor substrate 102. It is specifically contemplated that thepad layer 104 may be formed from a nitride, such as silicon nitride, butit should be understood that any appropriate material may be usedinstead. In addition, although the present embodiments are directed tothe formation of semiconductor fins for the purpose of forming, e.g.,fin field effect transistors (FinFETs), the material of the substrate102 dictates the material of the fins that will be formed, and anyappropriate material may be used to create fins for any purpose.

In one embodiment, the semiconductor substrate 102 is formed from abulk, silicon-containing material. Illustrative examples ofsilicon-containing materials suitable for the bulk-semiconductorsubstrate include, but are not limited to, silicon, silicon germanium,silicon carbide, silicon germanium carbide, polysilicon, epitaxialsilicon, amorphous silicon, and multi-layers thereof. Although siliconis the predominantly used semiconductor material in wafer fabrication,alternative semiconductor materials can be employed, such as, but notlimited to, germanium, gallium arsenide, gallium nitride, cadmiumtelluride, and zinc selenide. Although not depicted herein, thesemiconductor substrate 102 may also be a semiconductor on insulator(SOI) substrate.

Referring now to FIG. 2, a cross-sectional view of a step in forming asemiconductor device is shown. A set of mandrels 202 are deposited onthe pad layer 104. It is specifically contemplated that the mandrels 202may be formed from amorphous silicon, but any appropriate material maybe used instead. The mandrels 202 may formed using any appropriatelithographic process.

In one embodiment of a lithographic process, a hard mask may be used todefine the mandrels 202. The hardmask may be formed by first depositinga dielectric hard mask material, such as silicon nitride or silicondioxide, atop a layer of mandrel material and then applying aphotoresist pattern to the hard mask material by depositing aphotoresist material and illuminating regions of the photoresistmaterial with an appropriate light source. The illuminated regions ofthe photoresist material create a photoresist pattern that definesregions for the mandrels 202. The photoresist pattern is thentransferred into the hard mask material using, for example, a dry etchprocess. Next the photoresist pattern is removed and the hard maskpattern is then transferred into the mandrel material during a selectiveetching process. The hard mask may be removed by a wet or dry etch,leaving only the mandrels 202.

Referring now to FIG. 3, a cross-sectional view of a step in forming asemiconductor device is shown. An angled, directional deposition processis used to deposit spacers 304 on the top and on one lateral side ofeach mandrel 202. As shown, the angled, directional deposition processmeets the mandrels 202 at an angle, such that material on the lee sideof each mandrel 202 impacts the next mandrel 202 or accumulates on thepad layer 104.

It should be understood that any form of directional deposition may beused to deposit the spacers 304, but gas cluster ion beam (GCIB)deposition is specifically contemplated. In GCIB deposition, ahigh-pressure gas is allowed to expand in a vacuum and subsequentlycondense into clusters. The clusters can be ionized and directed onto asurface using magnets to provide a highly anisotropic deposition. Theangle of this gas cluster ion beam can be controlled to provide anyappropriate deposition angle. Exemplary materials that may be used inGCIB deposition include silane, ammonia, nitrogen, argon, oxygen,nitrogen trifluoride, tetrafluoromethane, diborane, phosphine, arsine,germane, methane, and others. The GCIB bombardment can penetrate asurface from about 2 nm to about 20 nm, implanting the GCIB species tosuch a depth where it may interact with the material of the surface.

It is specifically contemplated that the GCIB deposition process may useoxygen to oxidize the affected surfaces of the mandrels 202. The GCIBprocess may alternatively use precursor gasses that include oxygenincluding, e.g., carbon monoxide or carbon dioxide. Theseoxygen-containing precursors can additionally be combined with othermixture gasses such as nitrogen, helium, or similar, to vary clustersize and/or material conversion rate, or to create co-infused films,(e.g., oxygen/nitrogen gas mixtures to create silicon oxynitride). In aprocess using a pure oxygen beam, the mixture flow rate can be betweenabout 200 sccm and about 1,000 sccm through an expansion nozzle tocreate an atomic cluster having between about 100 and about 1000atoms/cluster. The acceleration voltage of these clusters will rangebetween about 1 kV to 80 kV, depending on the amount of materialconversion depth needed, resulting in an oxygen dose of ˜1×10¹² ions/cm²to about 1×10¹⁶ ions/cm². A pressure cell having a voltage rangingbetween about 1V to about 60 kV can then be applied to these clustersdirectly before wafer impact to break up clusters and reduce anysub-layer damage.

If the mandrels 202 are formed from amorphous silicon, then the spacers304 that result from a pure oxygen beam are formed from silicon dioxide.In an alternative embodiment, the GCIB deposition may be used todirectly deposit spacer material onto the surface of the mandrels 202 toform the spacers 304. It is specifically contemplated that spacers 304may be formed to a thickness of about 10 nm, but it should be understoodthat any appropriate thickness may be formed in accordance with designneeds.

The angle of GCIB bombardment can be between about 10° and about 80°,depending on the height and spacing of the mandrels 202, with tallermandrels necessitating the use of steeper angles. The angle ofbombardment can be set using electrostatic lenses and/or waferstaging—physically angling the wafer underneath an otherwise verticalbeam to achieve a specific angle.

Referring now to FIG. 4, a cross-sectional view of a step in forming asemiconductor device is shown. A mask 402 is deposited over one or moreof the uncovered mandrel sidewalls in regions where fins are not needed.It should be noted that the deposition of the mask 402 has a largemargin of error with respect to lithography process variations. As shownin FIG. 4, the mask 402 is unintentionally formed such that the mask 402runs over onto the next mandrel 202. Because the spacers 304 alreadyexist on the next mandrel 202, the presence of the mask 402 does notaffect whether fins will be formed in that region. The mask 402 maytherefore be made significantly smaller or larger without affecting theoutcome.

Referring now to FIG. 5, a cross-sectional view of a step in forming asemiconductor device is shown. The directional, angled depositionprocess is repeated, this time aimed in a direction that reaches thepreviously unexposed surfaces of the mandrels 202. For those surfaces,the spacer is extended to form spacer 504 that covers the entire mandrel202. However, for sidewalls that are covered by the mask 402, thedeposited species 502 cannot reach the sidewalls and no spacer isformed. As noted above, the directional, angled deposition process mayinclude GCIB deposition. In an alternative embodiment, an isotropicdeposition process may be used for the second spacer formationstep—because the mask 402 is in place, the isotropic etch will be unableto reach the second mandrel sidewall.

Referring now to FIG. 6, a cross-sectional view of a step in forming asemiconductor device is shown. The mask 402 is removed by anyappropriate etching process, such as a wet etch or a dry etch. Theremoval of the mask 402 exposes un-oxidized sidewall(s) 602, which lackspacer material. In contrast, other mandrels 202 are fully encapsulatedby spacer 504.

Referring now to FIG. 7, a cross-sectional view of a step in forming asemiconductor device is shown. An anisotropic etch, such as reactive ionetching (RIE), is used to remove spacer material from the horizontalsurfaces of the mandrels 202. This leaves spacers 702 on the sidewallsof the mandrels 202, with a gap on sidewall 602 where no spacer isformed.

RIE is a form of plasma etching in which during etching the surface tobe etched is placed on a radio-frequency powered electrode. Moreover,during RIE the surface to be etched takes on a potential thataccelerates the etching species extracted from plasma toward thesurface, in which the chemical etching reaction is taking place in thedirection normal to the surface. Other examples of anisotropic etchingthat can be used at this point of the present invention include ion beametching, plasma etching or laser ablation.

Referring now to FIG. 8, a cross-sectional view of a step in forming asemiconductor device is shown. The mandrels 202 have been removed usingany appropriate etch (e.g., a wet chemical etch), leaving the spacers702 standing. As can be seen in the figure, the spacers 702 in thisexample are evenly spaced, with the exception of a gap where the mask402 prevented spacers from being formed in the second angled,directional deposition.

Referring now to FIG. 9, a cross-sectional view of a step in forming asemiconductor device is shown. The spacers 702 are used as a mask for ananisotropic etch that forms semiconductor fins 902 from thesemiconductor substrate 102. The spacing between the fins 902 istherefore the same as the spacing between their respective spacers 702,with a gap 904 being left where no fin was formed. In this manner, fins902 can be formed at any appropriate spacing without the need to removeextraneous fins after formation, thereby preventing, for example,accidental removal of device fins.

Once the semiconductor fins 902 have been formed, a semiconductor devicemay be finished by, for example, forming a gate stack over a channelregion of a fin and forming source and drain regions at respective endsof the fin. This results in a fin field effect transistor (FinFET), withmany variations on the general FinFET design being available. Forexample, the source/drain regions of adjacent fins may be merged,different gate configurations are available, and other structuralmodifications may be made to the fins in accordance with device design.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments may include a design for an integrated circuitchip, which may be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer may transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Referring now to FIG. 10, a method for forming fins is shown. Block 1002forms the mandrels 202 on a substrate. The mandrels may be formed from,e.g., amorphous silicon using a photolithographic process. Block 1004forms spacers 302 on a first mandrel sidewall using an angled,directional process such as GCIB, where for example the side of themandrels 202 exposed to the GCIB process is oxidized by a beam of oxygento form silicon dioxide.

Block 1006 masks the second sidewall of the mandrels 202 in regionswhere no device fins are needed. This mask 402 may be formed using anyappropriate process and may touch a neighboring mandrel's spacer 302.Block 1008 forms spacers on the second mandrel sidewall, but only in theunmasked regions. In masked regions, the mask 402 blocks the angleddeposition from reaching the second sidewall. Block 1010 removes themask after the spacers 504 have been formed on unmasked mandrels 202.The previously masked mandrels have an exposed face 602.

Block 1012 removes the spacer material from horizontal mandrel surfacesusing, e.g., an anisotropic etch such as RIE. This etch leaves thespacers 702 along the vertical sidewalls of the mandrels 202. Block 1014then etches away the mandrels 202, such that the spacers 702 stand free.Block 1016 forms fins 902 from the substrate 102 using the spacers 702as a mask, performing a timed anisotropic etch to create fins 902 at theheight needed. Further processes may then be employed to form finishedsemiconductor devices from the fins 902.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A method of forming semiconductor fins,comprising: forming first spacers on a first sidewall of each of aplurality of amorphous silicon mandrels using an oxygen gas cluster ionbeam that is angled between about 10° and about 80°; masking a finlessregion by forming a mask directly on a second sidewall of one or more ofthe plurality of mandrels; isotropically forming second spacers on asecond sidewall of all unmasked mandrels using an oxygen gas cluster ionbeam; unmasking the finless region; anisotropically etching spacermaterial from horizontal surfaces of the mandrels after unmasking thefinless region; etching away the mandrels; and forming fins from asubstrate, comprising a nitride pad layer directly on a semiconductorlayer, using the first and second spacers as a mask, such that no finsare formed in the finless region.
 2. The method of claim 1, whereinmasking the finless region further comprises forming the mask todirectly contact a first spacer on an adjacent mandrel.
 3. The method ofclaim 1, wherein no fin is removed after formation of the fins.
 4. Themethod of claim 1, wherein the nitride pad layer includes siliconnitride.
 5. The method of claim 1, wherein the oxygen gas cluster ionbeam includes an angled deposition process.
 6. The method of claim 1,wherein unmasking the finless region includes unmasking the secondsidewall of the one or more of the plurality of mandrels.
 7. The methodof claim 1, further comprising patterning a mandrel material using ahard mask to form the plurality of amorphous silicon mandrels prior toforming the first spacers.
 8. The method of claim 1, wherein the firstspacers on the first sidewall include silicon dioxide.
 9. The method ofclaim 1, wherein masking the finless region includes forming the mask inregions where the fins are not needed.
 10. The method of claim 1,wherein forming the second spacers encapsulates all the unmaskedmandrels in spacer material from the first and second spacers.
 11. Themethod of claim 1, wherein unmasking the finless region exposes thesecond sidewall on all masked madrels.
 12. A method of formingsemiconductor fins, comprising: forming first spacers on a firstsidewall of each of a plurality of amorphous silicon mandrels using anoxygen gas cluster ion beam that is angled between about 10° and about80°; masking a finless region by forming a mask directly on a secondsidewall of one or more of the plurality of mandrels; isotropicallyforming second spacers on a second sidewall of all unmasked mandrelsusing an oxygen gas cluster ion beam; unmasking the finless region toexpose the second sidewall on all masked madrels; anisotropicallyetching spacer material from horizontal surfaces of the mandrels afterunmasking the finless region; etching away the mandrels; and formingfins from a substrate, comprising a silicon nitride pad layer directlyon a semiconductor layer, using the first and second spacers as a mask,such that no fins are formed in the finless region.
 13. The method ofclaim 12, wherein masking the finless region further comprises formingthe mask to directly contact a first spacer on an adjacent mandrel. 14.The method of claim 12, wherein no fin is removed after formation of thefins.
 15. The method of claim 12, wherein the oxygen gas cluster ionbeam includes an angled deposition process.
 16. The method of claim 12,wherein unmasking the finless region includes unmasking the secondsidewall of the one or more of the plurality of mandrels.
 17. The methodof claim 12, further comprising patterning a mandrel material using ahard mask to form the plurality of amorphous silicon mandrels prior toforming the first spacers.
 18. The method of claim 12, wherein the firstspacers on the first sidewall include silicon dioxide.
 19. The method ofclaim 12, wherein masking the finless region includes forming the maskin regions where the fins are not needed.
 20. The method of claim 12,wherein forming the second spacers encapsulates all the unmaskedmandrels in spacer material from the first and second spacers.